The present invention relates to an exhaust energy recovery and generator device for use with an engine (referred to hereinafter as a "generator device").
Internal combustion engines, such as gasoline engines and diesel engines, produce a power output by combusting fuel in cylinders to generate an energy with which the pistons are lowered. An exhaust gas produced by the combustion of the fuel in the cylinder is discharged through an exhaust manifold into the atmosphere. The exhaust gas has a high temperature and a high pressure and still retains a considerable amount of energy.
There has recently been developed a thermally insulative internal combustion engine with various parts constructed of ceramics, including an outer wall of an exhaust manifold, a cylinder liner, a heat-insulative plate on a cylinder head, an exhaust valve, and a piston, for example. This type of internal combustion engine is not designed to radiate heat generated therein to cool the engine, but is rather designed to recover the energy of an exhaust gas which is of a higher temperature than that of the exhaust gas emitted from conventional engines, thus increasing the operation efficiency of the engine. One conventional exhaust energy recovery device includes a turbine disposed near an exhaust port and rotatable by an exhaust gas for producing excessive rotative power which is reduced in speed by a number of speed reducer gears and fed back to a crank shaft. However, the prior exhaust energy recover device has been disadvantageous and ineffective in that it is complex in overall construction, making the internal combustion engine costly, has a poor operation efficiency, and cannot be used under a partial load.
There is known another exhaust energy recovery device for use with an ordinary engine having an engine cooling device, rather than with the thermally insulative engine. The exhaust energy recovery device has a turbine disposed near an exhaust port and rotatable by an exhaust gas, and an air compressor rotatable by the turbine for feeding air under pressure into an intake manifold to increase the engine operation efficiency when the engine rotates at a high speed and under a high load. The turbine is required to operate at high speeds for supplying compressed air effective for high engine rotational speeds. However, the turbine fails to supply such effective compressed air when the exhaust gas flows at a low speed, that is, the turbine cannot feed air into the engine when the engine rotates at a low speed and under a high load. Another drawback is that when the engine rotates at a high speed, the turbine tends to supply an excessive amount of air under pressure into the engine, and it is necessary to discharge a portion of the exhaust gas through a bypass passage into the atmosphere. Such a bypass passage discharges the entire exhaust energy into the atmosphere when the engine rotates at a low speed. Accordingly, the exhaust energy recovery device fails to utilize the exhaust energy effectively.
According to the process of recovering the exhaust gas energy from an internal combustion engine in the form of a torque or power, as described above, the exhaust turbine is rotated by the exhaust gas energy, and rotative power from the exhaust turbine is applied through a train of gears to the crank shaft of the engine.
With the above exhaust energy recovery process, however, the turbine cannot respond well to variations in the speed of flow of the exhaust gas. The speed reducer required to reduce the high speed of rotation of the exhaust turbine has not yet been practically available since it would be highly complex in construction and reduce the efficiency of transmitting power.
There have heretofore been used induction generators to be driven by exhaust turbines, the induction generators having permanent magnet rotors to withstand centrifugal forces applied thereto. However, limitations have been imposed on the speed of rotation of the rotor due to the strength of the magnet and weak magnetic forces thereof when the rotor is to be rotated at high speeds. As a consequence, it has been difficult to manufacture a high-power generator of this type.
Generators generate greater electric power as the rotor rotates at a higher speed. Therefore, the generators as they are driven by exhaust turbines rotated at high speeds by the exhaust energy are most effective means for efficiently utilizing the exhaust energy.
For driving a synchronous generator with an exhaust turbine and supplying regenerative energy to an internal combustion engine, it has been customary to pick up an induced voltage from a rotor winding through a brush or from a stator winding disposed around the permanent magnet rotor. Such an arrangement causes no problem if incorporated in an ordinary generator having a rotor speed of about 3,000 rpm. However, if a rotor speed were 20,000 rpm or higher, then the generator would be damaged due to increased friction, or frictional or sliding shocks.
The generator with the permanent magnet cannot generate a sufficiently large amount of electric power and hence cannot have a large power generation capacity since the permanent magnet of metal produces only small magnetic forces.